Photocurable composition and cured material thereof

ABSTRACT

The present invention provides a photocurable composition containing an ultraviolet absorber, which has high photocurability and yields a cured material having a high cutting capacity against ultraviolet rays from the outside, a low yellow index, and colorlessness and transparency. The present invention relates to a sheet-shaped photocurable composition which includes the following components (A) to (D), and when a cured material obtained after photocuring the photocurable composition has a thickness of 150 μm, a yellow index of the cured material is 4.0 or less and a light transmittance of the cured material at a wavelength of 385 nm is 5.0% or less: a component (A): a (meth)acrylate compound, a component (B): a film forming resin, a component (C): a photoinitiator, and a component (D): an ultraviolet absorber.

TECHNICAL FIELD

The present invention relates to a photocurable composition and a cured material thereof. More specifically, the present invention relates to a photocurable composition including an ultraviolet absorber, which can form a cured material that hardly transmits ultraviolet rays from the outside after curing and causes less coloring.

BACKGROUND ART

In recent years, organic EL elements have attracted attention as a light emitting element which can perform high-luminance light emission by a low-voltage direct current drive.

Furthermore, WO 2015/098647 A (corresponding to US 2016/0,329,522 A) describes that organic layers such as a light emitting layer and the like of an organic EL element have a problem in easy deterioration of transparency by ultraviolet rays. Then, this publication proposes a technique of coating an organic EL layer and an organic EL element with a resin layer containing an ultraviolet absorber.

SUMMARY OF INVENTION

However, the resin layer described in WO 2015/098647 A (corresponding to US 2016/0,329,522 A) is constituted with an elastomer or rubber, and thus, in the first place, there is a problem that the organic EL element and the organic EL layer as an adherend are damaged due to heating during compression bonding. In addition, there is a risk that the organic EL element and the organic EL layer may be deteriorated in a reliability test due to an effect of uncured components.

On the other hand, in a case where a resin layer containing an ultraviolet absorber is formed of a photocurable resin having a high adhesive force, not of an elastomer or rubber, as a main component, a problem due to heating during compression bonding does not occur. However, even in such a resin layer, it is difficult to form a colorless and transparent cured material from the viewpoint that the ultraviolet absorber itself causes coloring. Furthermore, in the worst case, there is a problem that the photocurability is deteriorated due to an unfavorable effect of the ultraviolet absorber in some cases. In addition, from the viewpoint that there is a demand for colorlessness and transparency for application to a display device such as an organic EL element and the like, a curable resin that involves coloring cannot be used for the application.

As described above, from the viewpoint that a photocurable composition to which an ultraviolet absorber had been added had low photocurability and made it difficult to form a colorless and transparent cured material in the related art, it was difficult to form the composition which could be applied to a display device such as an organic EL element and the like.

The present inventors have conducted intensive studies in order to accomplish the object, and as a result, they have discovered a method relating to a photocurable composition which contains an ultraviolet absorber and is substantially colorless and transparent (that is, has high transparency in the visible region), thereby leading to completion of the present invention.

That is, according to the present invention, provided is a photocurable composition containing an ultraviolet absorber, which has high photocurability and yields a cured material thereof having a high cutting capability against ultraviolet rays from the outside, a low yellow index, and colorlessness and transparency.

DESCRIPTION OF EMBODIMENTS

Hereinafter, embodiments of the present invention will be described. Furthermore, the present invention is not limited to the following embodiments. In the present specification, in an expression with “to” or “from” indicating a range from an upper limit value to a lower limit value, the range also includes the upper and lower limit values themselves. That is, “X to Y” or “from X to Y” indicating the range includes X and Y, and means “X or more and Y or less”. In addition, operations and measurements of physical properties and the like are performed under conditions of room temperature (20 to 25° C.)/a relative humidity of 40 to 50% RH unless otherwise specified.

Moreover, in the present specification, an acryloyl group and a methacryloyl group are collectively referred to as a (meth)acryloyl group. Furthermore, a compound having a (meth)acryloyl group is also referred to as (meth)acrylate. In addition, similarly, a compound and the like including (meth), such as (meth)acrylic acid and the like are also generic terms for a compound having “meth” and a compound not having “meth” in the names.

Furthermore, in the present specification, a photocurable composition before curing, which has been processed into a sheet shape, is referred to as a “sheet-shaped photocurable composition”. In addition, a “cured material” refers to a product obtained by subjecting a photocurable composition to polymerization by irradiation with light in a state where the composition does not include a solvent.

One aspect of the present invention relates to the following [1]:

A sheet-shaped photocurable composition which includes the following components (A) to (D), and when a cured material obtained after photocuring the photocurable composition has a thickness of 150 μm, a yellow index of the cured material is 4.0 or less and a light transmittance of the cured material at a wavelength of 385 nm is 5.0% or less:

a component (A): a (meth)acrylate compound,

a component (B): a film forming resin,

a component (C): a photoinitiator, and

a component (D): an ultraviolet absorber.

Moreover, the present invention also includes aspects according to the following [2] to [9] as non-limiting examples of preferred aspects.

[2] The sheet-shaped photocurable composition as described in [1], in which the component (D) is a compound represented by the general formula 1 which will be described later.

[3] The sheet-shaped photocurable composition as described in [1] or [2], in which the amount of the component (D) is 0.1 to 5.0 parts by mass with respect to 100 parts by mass of the total mass of the components (A) to (C).

[4] The sheet-shaped photocurable composition as described in any one of [1] to [3], further including the following component (E), and when a cured material obtained after photocuring the photocurable composition has a thickness of 150 μm, a yellow index of the cured material is 3.0 or less and a light transmittance of the cured material at a wavelength of 385 nm is 5.0%:

a component (E): an auxiliary ultraviolet absorber that is an ultraviolet absorber not corresponding to the component (D) (that is, excluding the component (D)).

[5] The sheet-shaped photocurable composition as described in [4], in which the component (E) is a compound represented by the general formula 2 which will be described later.

[6] The sheet-shaped photocurable composition as described in [4] or [5], in which the total of the component (D) and the component (E) is 0.1 to 3.0 parts by mass with respect to 100 parts by mass of the total mass of the components (A) to (C).

[7] The sheet-shaped photocurable composition as described in any one of [1] to [6], in which the component (A) includes a (meth)acrylate oligomer and a (meth)acrylate monomer.

[8] The sheet-shaped photocurable composition as described in any one of [1] to [7], in which the component (B) is a phenoxy resin.

[9] A cured material of the sheet-shaped photocurable composition as described in any one of [1] to [8].

<Photocurable Composition and Method for Preparing the Same>

One aspect of the present invention relates to a sheet-shaped photocurable composition including the components (A) to (D). According to one aspect of the present invention, provided is a sheet-shaped photocurable composition containing an ultraviolet absorber, which has high photocurability and yields a cured material thereof having a high cutting capability against ultraviolet rays from the outside, a low yellow index, and colorlessness and transparency. That is, with the sheet-shaped photocurable composition according to one aspect of the present invention, the photocurability is not decreased even with the addition of an ultraviolet absorber. Moreover, with the photocurable composition, it is possible to form a cured material which can cut ultraviolet rays from the outside, has a low yellow index, and is substantially colorless and transparent. In addition, a display element can reproduce the original color even when the photocurable composition has been applied thereto, and therefore, the photocurable composition can be suitably used for a display device such as an organic EL and the like.

The sheet-shaped photocurable composition according to one aspect of the present invention is that, when a cured material obtained after photocuring the photocurable composition has a thickness of 150 μm, a yellow index (yellowness) of the cured material is 4.0 or less and a light transmittance of the cured material at a wavelength of 385 nm is 5.0% or less. Furthermore, the yellow index is more preferably 3.5 or less, still more preferably 3.0 or less, and particularly preferably 2.5 or less (lower limit value of 0). In addition, the light transmittance at a wavelength of 385 nm is more preferably 3% or less, still more preferably 1% or less, and particularly preferably 0.5% or less (lower limit value of 0%).

Hereinbelow, the respective components of the photocurable composition will be described in detail. However, the present invention is not limited thereto.

[Component (A)]

The component (A) which can be used in one aspect of the present invention is a compound having a (meth)acryloyl group as a functional group ((meth)acrylate compound). As the component (A), a combination of an oligomer and a monomer is preferable from the viewpoint of improving the adhesive force and adjusting the viscosity.

The weight-average molecular weight of the oligomer is not particularly limited, but is preferably 10,000 to 100,000, more preferably 25,000 to 90,000, and particularly preferably 30,000 to 80,000. When the weight-average molecular weight is 10,000 or more, the curability is improved. In addition, when the weight-average molecular weight is 100,000 or less, the viscosity is lower and the affinity at an interface at a time of being adhered to an adherend is improved. Here, the weight-average molecular weight of the oligomer refers to a weight-average molecular weight in terms of polystyrene, as measured by gel permeation chromatography.

As the oligomer which can be used in the component (A), a (meth)acrylate oligomer is preferable, and from the viewpoint of improving the adhesive force, a urethane-modified (meth)acrylate oligomer is more preferable, and a urethane-modified (meth)acrylate oligomer having a polycarbonate in a main skeleton is particularly preferable.

As the urethane-modified (meth)acrylate oligomer, either a synthetic product or a commercially available product may be used. Specific examples of the commercially available product include, but are not limited to, UN-004RU manufactured by Negami Chemical Industrial Co., Ltd., and the like.

The urethane-modified (meth)acrylate oligomer can be synthesized from, for example, a reaction product of (i) a polyol compound having two or more hydroxyl groups in the molecule, (ii) a compound having two or more isocyanate groups in the molecule, and (iii) a (meth)acrylate containing at least one or more hydroxyl groups in the molecule.

The compound having two or more isocyanate groups in the molecule in (i) is not particularly limited, but examples thereof include an aromatic polyisocyanate, an alicyclic polyisocyanate, an aliphatic polyisocyanate, and the like.

The aromatic polyisocyanate is not particularly limited, but examples thereof include 2,4-tolylene diisocyanate, 2,6-tolylene diisocyanate, 1,3-xylylene diisocyanate, 1,4-xylylene diisocyanate, tetramethylxylylene diisocyanate, diphenylmethane diisocyanate, naphthalene-1,5-diisocyanate, triphenylmethane triisocyanate, and the like.

The alicyclic polyisocyanate is not particularly limited, but examples thereof include isophorone diisocyanate, bis(4-isocyanatocyclohexyl)methane, 1,3-bis(isocyanatomethyl)cyclohexane, 1,4-bis(isocyanatomethyl)cyclohexane, norbornane diisocyanate, bicycloheptane triisocyanate, and the like.

The aliphatic polyisocyanate is not particularly limited, but examples thereof include hexamethylene diisocyanate, 1,3,6-hexamethylene triisocyanate, 1,6,11-undecatriisocyanate, and the like. Among these, diisocyanates such as isophorone diisocyanate, hexamethylene diisocyanate, and the like are preferable.

Among those, the aliphatic polyisocyanate and the alicyclic polyisocyanate are preferable from the viewpoint of obtaining a cured material having flexibility. These may be used singly or in combination of a plurality thereof.

The polyol compound having two or more hydroxyl groups in the molecule in (ii) is not particularly limited, but examples thereof include polyether polyol, polyester polyol, caprolactone diol, bisphenol polyol, polyisoprene polyol, hydrogenated polyisoprene polyol, polybutadiene polyol, hydrogenated polybutadiene polyol, castor oil polyol, polycarbonatediol, and the like. Among these, polycarbonate diol, polybutadiene polyol, or hydrogenated polybutadiene polyol is preferable from the viewpoint of excellent transparency and endurance, and polycarbonate diol is particularly preferable from the viewpoint that it does not cause white turbidity of a cured material in an atmosphere with a high temperature and a high humidity. That is, a urethane-modified (meth)acrylate oligomer having a polycarbonate in the main skeleton, which is synthesized using the polycarbonate diol, can be preferably used as the component (A) from the viewpoint that it hardly causes occurrence of white turbidity of a cured material in an atmosphere with a high temperature and a high humidity. These may be used singly or in combination of a plurality thereof.

The (meth)acrylate containing at least one or more hydroxyl groups in the molecule in (iii) is not particularly limited, but examples thereof include mono(meth)acrylates of dihydric alcohols such as ethylene glycol, propylene glycol, 1,3-propanediol, 1,3-butanediol, 1,4-butanediol, polyethylene glycol, and the like; mono(meth)acrylates or di(meth)acrylates of trihydric alcohols such as trimethylolethane, trimethylolpropane, glycerin, and the like; and so on. Among these, the mono(meth)acrylates of dihydric alcohols are preferable, and the mono(meth)acrylate of ethylene glycol is more preferable, from the viewpoint that a cured material having excellent flexibility can be obtained. These may be used singly or in combination of a plurality thereof.

A method for synthesizing the urethane-modified (meth)acrylate oligomer is not particularly limited, and a known method can be used. Examples thereof include the following methods. First, the polyol compound having two or more hydroxyl groups in the molecule (i) and the isocyanate compound having two or more isocyanate groups in the molecule (ii) are reacted in a diluent to obtain a urethane prepolymer. At this time, a molar ratio of the compound of (i) to the compound of (ii) (the polyol compound: the isocyanate compound) is not particularly limited, but is preferably 3:1 to 1:3, and more preferably a ratio of 2:1 to 1:2. Furthermore, the diluent is not particularly limited, but examples thereof include methyl ethyl ketone, methoxyphenol, and the like. Then, the isocyanate groups remaining in the obtained urethane prepolymer are reacted with the (meth)acrylate containing at least one or more hydroxyl groups in the molecule (iii) in a sufficient amount for a reaction with the isocyanate groups to synthesize a urethane (meth)acrylate oligomer.

Moreover, a catalyst used in the synthesis is not particularly limited, but examples thereof include lead oleate, tetrabutyltin, antimony trichloride, triphenyl aluminum, trioctyl aluminum, dibutyltin dilaurate, copper naphthenate, zinc naphthenate, zinc octoate, zinc octenoate, zirconium naphthenate, cobalt naphthenate, tetra-n-butyl-1,3-diacetyloxydistannoxane, triethylamine, 1,4-diaza[2,2,2]bicyclooctane, N-ethylmorpholine, and the like, and among these, dibutyltin dilaurate, zinc naphthenate, zinc octoate, and zinc octenoate are preferable from the viewpoint that a cured material having a high activity and a more excellent transparency can be obtained. It is preferable that these catalysts are used in the amount of 0.0001 to 10 parts by mass with respect to 100 parts by mass of the total mass of the reactants. In addition, the reaction temperature is usually preferably 10 to 100° C., and particularly preferably 30 to 90° C.

The urethane-modified (meth)acrylate oligomer may be used after being diluted with a solvent or a monomer which will be described later, in a step in which the oligomer is used as a raw material for the photocurable composition.

These oligomers may be used singly or in combination of a plurality thereof.

Examples of the monomer which can be used as the component (A) include monofunctional, bifunctional, trifunctional, or tetrafunctional or higher polyfunctional monomers. A (meth)acrylate monomer is preferable, and a bifunctional (meth)acrylate monomer is particularly preferable.

The molecular weight of the monomer is not particularly limited, but from the viewpoint that the viscosity of the photocurable composition is lowered, the molecular weight is preferably less than 10,000, more preferably 5,000 or less, still more preferably 1,500 or less, and particularly preferably 1,000 or less. Here, the molecular weight of the monomer refers to a sum of atomic weights.

The monofunctional monomer is not particularly limited, but examples thereof include lauryl(meth)acrylate, stearyl (meth)acrylate, tetrahydrofurfuryl (meth)acrylate, caprolactone-modified tetrahydrofurfuryl (meth)acrylate, cyclohexyl (meth)acrylate, dicyclopentanyl (meth)acrylate, isobornyl (meth)acrylate, benzyl (meth)acrylate, phenyl (meth)acrylate, phenoxyethyl (meth)acrylate, phenoxydiethylene glycol (meth)acrylate, phenoxytetraethylene glycol (meth)acrylate, nonylphenoxyethyl (meth)acrylate, butoxyethyl (meth)acrylate, 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, glycerol (meth)acrylate, modified butyl (meth)acrylate, epichlorohydrin-modified phenoxy(meth)acrylate, N,N-dimethylaminoethyl (meth)acrylate, N,N-diethylaminoethyl (meth)acrylate, morpholino(meth)acrylate, polyethylene glycol mono(meth)acrylate, polypropylene glycol mono(meth)acrylate, polyoxytetramethylene glycol mono(meth)acrylate, and the like.

The bifunctional monomer is not particularly limited, but examples thereof include neopentyl glycol di(meth)acrylate, bisphenol A di(meth)acrylate, epichlorohydrin-modified bisphenol A di(meth)acrylate, stearic acid-modified pentaerythritol di(meth)acrylate, dicyclopentenyl di(meth)acrylate, di(meth)acryloyl isocyanurate, polyethylene glycol di(meth)acrylate, polypropylene glycol di(meth)acrylate, polyoxytetramethylene glycol di(meth)acrylate, and the like.

The trifunctional monomer is not particularly limited, but examples thereof include trimethylolpropane tri(meth)acrylate, pentaerythritol tri(meth)acrylate, epichlorohydrin-modified trimethylolpropane tri(meth)acrylate, epichlorohydrin-modified glycerol tri(meth)acrylate,tris(acryloyloxyethyl)isocyanurate, and the like.

The tetrafunctional or higher polyfunctional monomer is not particularly limited, but examples thereof include ditrimethylolpropane tetra(meth)acrylate, pentaerythritol tetra(meth)acrylate, dipentaerythritol monohydroxypenta(meth)acrylate, alkyl-modified dipentaerythritol penta(meth)acrylate, dipentaerythritol hexa(meth)acrylate, and the like. These polymerizable monomers may be used singly or in combination of a plurality thereof.

Among these, as the monomer, the mono-to hexa-functional monomers are preferable, the mono- to tri-functional monomer is more preferable, the mono- or bi-functional monomers are still more preferable, and the bi-functional monomer is particularly preferable.

Furthermore, as the monomer, (meth)acrylate containing an ether bond and a (meth)acryloyl group is preferable, and a polyether monomer having 8 to 30 repeating structures of the ether bonds in one molecule (polyether (meth)acrylate having 8 to 30 repeating structures of the ether bonds in one molecule) is the most preferable. In a case where there are 8 or more repeating structures of the ether bonds, it becomes more difficult for the white turbidity of a cured material due to separation from moisture permeating from the outside into the cured material to occur in an atmosphere with a high temperature and a high humidity. On the other hand, in a case where there are 30 or less repeating structures of the ether bonds, it becomes more difficult for the polyether monomers to be crystallized with the same kinds of the polyether monomers, and it also becomes more difficult for the white turbidity of the cured material to occur.

The (meth)acrylate containing an ether bond and a (meth)acryloyl group is not particularly limited, but examples thereof include polyethylene glycol mono(meth)acrylate, polyethylene glycol di(meth)acrylate, polypropylene glycol mono(meth)acrylate, polypropylene glycol di(meth)acrylate, polyoxytetramethylene glycol mono(meth)acrylate, polyoxytetramethylene glycol di(meth)acrylate, and the like. Among these, polyethylene glycol di(meth)acrylate is preferable, and polyethylene glycol dimethacrylate is more preferable.

The molecular weight of the (meth)acrylate containing an ether bond and a (meth)acryloyl group is preferably in the range of 200 to 5,000, more preferably 250 to 3,000, and still more preferably 300 to 1,500.

As the (meth)acrylate containing an ether bond and a (meth)acryloyl group, either a commercially available product or a synthetic product may be used. Specific examples of the commercially available product include, but are not limited to, NKESTER (trademark) series M-90G, AM-130G, M-230G, A-400, A-600, APG-700, A-1000, 9G, 14G, 23G, 1206PE, and the like, manufactured by Shin-Nakamura Chemical Co., Ltd., BLEMMER (registered trademark) series PDE-600, PDP-700, ADE-600, and the like, manufactured by NOF Corporation, LIGHT ESTER series 130MA, 130A, 14EG, 14EG-A, and the like, manufactured by Kyoeisha Chemical Co., Ltd.

The number of functional groups (the number of (meth)acryloyl groups) of the monomer may be 1 or more, and these may be used singly or in combination of a plurality thereof.

The monomer used for dilution of the urethane-modified (meth)acrylate oligomer is not particularly limited, but from the viewpoint of decreasing the viscosity of a photocurable composition and improving the handling properties, it is preferably a monofunctional alicyclic (meth)acrylate, a bifunctional alicyclic (meth)acrylate, a trifunctional alicyclic (meth)acrylate or a polyfunctional alicyclic (meth)acrylate such as a tetrafunctional or higher functional alicyclic (meth)acrylate, more preferably the monofunctional alicyclic (meth)acrylate, still more preferably isobornyl (meth)acrylate, and particularly preferably isobornyl methacrylate.

From the viewpoint of decreasing the viscosity of the photocurable composition and improving the handling properties, the blending amount (addition amount, content) of the monomer is preferably 200 parts by mass or less, more preferably 100 parts by mass or less, and still more preferably 50 parts by mass or less with respect to 100 parts by mass of the oligomer. Further, the blending amount (addition amount, content) of the monomer is preferably more than 0 part by mass.

[Component (B)]

The component (B) which can be used in one aspect of the present invention is a film forming resin. The component (A) is liquid at 25° C. in many cases, whereas the component (B) is solid or has almost no fluidity at 25° C., and therefore, the component (B) is added in order to enable a photocurable composition to be formed in a sheet shape in an atmosphere at 25° C. Therefore, the sheet-shaped photocurable composition according to one aspect of the present invention has no fluidity at 25° C., and unlike the photocurable composition which is liquid at 25° C., the composition does not overflow from an end part of an adherend when used to stick plate-shaped adherends.

Specific examples of the component (B) are not particularly limited, and include known thermoplastic resins, known elastomers, and the like but the presence or absence of a reactive functional group such as an epoxy group and the like is not particularly limited.

Among those, a particularly preferable component (B) is a phenoxy resin. The phenoxy resin is, for example, a polymer synthesized from bisphenol A and epichlorohydrin, or a polymer obtained by polymerizing a polyfunctional epoxy resin such as a bisphenol type epoxy resin and the like.

Specific examples of the phenoxy resin are not particularly limited, but examples thereof include a bisphenol type phenoxy resin, a novolac type phenoxy resin, a naphthalene type phenoxy resin, a biphenyl type phenoxy resin, and the like. These may be used singly or in combination of a plurality thereof. As the phenoxy resin, the bisphenol type phenoxy resin is preferable from the viewpoint of good adhesion to a glass or a plastic of a protective panel. Among these, a mixture of a bisphenol A type phenoxy resin and a bisphenol F type phenoxy resin, or a phenoxy resin which is a copolymer of a bisphenol A type epoxy resin (phenoxy resin) and a bisphenol F type epoxy resin (phenoxy resin) is preferable, and the mixture of a bisphenol A type phenoxy resin and a bisphenol F type phenoxy resin is more preferable, from the viewpoint of good compatibility with the component (A) according to one aspect of the present invention. These may be used singly or in combination of a plurality thereof.

The weight-average molecular weight of the phenoxy resin is not particularly limited, but is preferably 10,000 to 100,000. Here, the weight-average molecular weight of the phenoxy resin refers to a weight-average molecular weight in terms of polystyrene, as measured by gel permeation chromatography.

As the phenoxy resin of the component (B), either a commercially available product or a synthetic product may be used. Specific examples of the commercially available product include, but are not limited to, Phenotote (registered trademark) series YP-50, YP-505, YP-55, YP-70, ZX-1356-2, FX-316, and the like, manufactured by NIPPON STEEL Chemical & Material Co., Ltd., jER (registered trademark) series 1256, 4250, 4275, and the like, manufactured by Mitsubishi Chemical Corporation, and PKHB, PKHC, PKHH, PKHJ, PKFE, and the like, manufactured by Tomoe Engineering Co., Ltd.

The component (B) may be used after being diluted with a solvent in a step in which it is used as a raw material for the photocurable composition.

The addition amount of the component (B) in the photocurable composition is not particularly limited, but is preferably 1 to 50 parts by mass, more preferably 5 to 45 parts by mass, and still more preferably 10 to 40 parts by mass with respect to 100 parts by mass of the component (A). When the addition amount is 1 part by mass or more, the film forming property is further improved, the occurrence of stickiness of the photocurable composition is further suppressed, and the peelability of a mold-released film or the like is further improved. In addition, when the addition amount is 50 parts by mass or less, the brittleness of a cured material is further improved.

[Component (C)]

The component (C) used in one aspect of the present invention is a photoinitiator. The photoinitiator is a compound that decomposes upon irradiation with active energy rays such as ultraviolet rays, visible light, and the like to generate a radical species, a cation species, or an anion species.

The component (C) is not particularly limited, but examples thereof include an acetophenone-based photoinitiator, a benzoin-based photoinitiator, a benzophenone-based photoinitiator, a thioxanthone-based photoinitiator, an acylphosphine oxide-based photoinitiator, and the like. These may be used singly or in combination of two or more kinds thereof.

The acetophenone-based photoinitiator is not particularly limited, but examples thereof include diethoxyacetophenone, 2-hydroxy-2-methyl-1-phenylpropan-1-one, benzyldimethylketal, 4-(2-hydroxyethoxy)phenyl-(2-hydroxy-2-propyl)ketone, 1-hydroxycyclohexylphenylketone, 2-methyl-2-morpholino(4-thiomethylphenyl)propan-1-one, 2-benzyl-2-dimethylamino-1-(4-morpholinophenyl)butanone, a 2-hydroxy-2-methyl-1-[4-(1-methylvinyl)phenyl]propanone oligomer, and the like. These may be used singly or in combination of two or more kinds thereof.

The benzoin-based photoinitiator is not particularly limited, but examples thereof include benzoin, benzoin methyl ether, benzoin ethyl ether, benzoin isopropyl ether, benzoin isobutyl ether, and the like. These may be used singly or in combination of two or more kinds thereof.

The benzophenone-based photoinitiator is not particularly limited, but examples thereof include benzophenone, methyl o-benzoylbenzoate, 4-phenylbenzophenone, 4-benzoyl-4′-methyl-diphenylsulfide, 3,3′,4,4′-tetra(t-butylperoxycarbonyl)benzophenone, 2,4,6-trimethylbenzophenone, 4-benzoyl-N,N-dimethyl-N-[2-(1-oxo-2-propenyloxy)ethyl]b enzenemethanaminium bromide, and (4-benzoylbenzyl)trimethylammonium chloride. These may be used singly or in combination of two or more kinds thereof.

The thioxanthone-based photoinitiator is not particularly limited, but examples thereof include 2-isopropylthioxanthone, 4-isopropylthioxanthone, 2,4-diethylthioxanthone, 2,4-dichlorothioxanthone, 1-chloro-4-propoxythioxanthone, 2-(3-dimethylamino-2-hydroxy)-3,4-dimethyl-9H-thioxantho n-9-one methochloride, and the like. These may be used singly or in combination of two or more kinds thereof.

The acylphosphine oxide-based photoinitiator is not particularly limited, but examples thereof include bis(2,4,6-trimethylbenzoyl)-phenylphosphine oxide, 2,4,6-trimethylbenzoyl-diphenylphosphine oxide, 2,4,6-trimethylbenzoylphenylethoxyphosphine oxide, and the like. These may be used singly or in combination of two or more kinds thereof.

Among these, the acylphosphine oxide-based photoinitiator is preferably included since it is easily cured with energy rays in the visible region and the photocurability is improved. However, it is preferable to add an appropriate amount of the acylphosphine oxide-based photoinitiator from the viewpoint that the photocurable composition itself may become yellow in some cases with an excessive addition of the acylphosphine oxide-based photoinitiator to the photocurable composition. Among the acylphosphine oxide photoinitiators, 2,4,6-trimethylbenzoyl-diphenylphosphine oxide is particularly preferable.

As the photoinitiator, either a commercially available product or a synthetic product may be used. Specific examples of the commercially available products include, but are not limited to, IRGACURE (registered trademark) series TPO and the like, manufactured by BASF.

The addition amount (content) of the component (C) in the photocurable composition is not particularly limited, but is preferably 0.1 to 5.0 parts by mass, more preferably 0.5 to 4.0 parts by mass, and still more preferably 1.0 to 3.0 parts by mass with respect to 100 parts by mass of the component (A). When the addition amount is 0.1 parts by mass or more, the photocurability is better exhibited. Further, when the addition amount is 5.0 parts by mass or less, the photocurable composition is less likely to become colored.

[Component (D)]

The component (D) used in one aspect of the present invention is an ultraviolet absorber. The yellow index and the light transmittance in a cured material of the photocurable composition are preferably controlled by the type and the amount of the ultraviolet absorber. Therefore, the component (D) is not particularly limited, but is preferably an ultraviolet absorber which can allow a yellow index of a cured material of a sheet-shaped photocurable composition including the component (D) in addition to the components (A) to (C) to be 4.0 or less and a light transmittance of the cured material at a wavelength of 385 nm to be 5.0% or less when the cured material is obtained after photocuring the composition and has a thickness of 150 μm. In other words, in a case where the component (D) is added to the sheet-shaped photocurable composition including the components (A) to (C), it is preferably an ultraviolet absorber which can allow the yellow index and the light transmittance at a wavelength of 385 nm to be each in ranges. The yellow index is more preferably 3.5 or less, still more preferably 3.0 or less, and particularly preferably 2.5 or less (lower limit value of 0). In addition, the light transmittance at a wavelength of 385 nm is more preferably 3% or less, still more preferably 1% or less, and particularly preferably 0.5% or less (lower limit value of 0%).

Furthermore, the ultraviolet absorber relating to the component (D) is not particularly limited, but is preferably a compound represented by the following general formula 1.

Here, R¹ _(n) represents the presence of n R¹ groups, R¹'s each independently represent a hydrocarbon group, and n represents an integer of 0 to 4.

Here, the hydrocarbon group is not particularly limited, but is preferably a hydrocarbon group having 1 to 8 carbon atoms, more preferably a hydrocarbon group having 1 to 4 carbon atoms, still more preferably a hydrocarbon group having 1 carbon atom (methyl group) or a hydrocarbon group having 4 carbon atoms, and particularly preferably a methyl group or a tert-butyl group. In addition, n is preferably 1, 2 or 3, more preferably 1 or 2, and still more preferably 2.

Moreover, the compound represented by the general formula 1 may also include a derivative thereof in which hydrogen in the main skeleton represented by the general formula 1 is substituted with another organic group. However, it is not construed to include a multimer in which a plurality of the structures represented by the general formula 1 are bonded to each other.

Specific examples of the component (D) include, but are not limited to, 2-(5-chloro-2-benzotriazolyl)-6-tert-butyl-p-cresol and the like.

As the component (D), either a commercially available product or a synthetic product may be used. Specific examples of the commercially available product include, but are not limited to, ADEKA STAB (registered trademark) series LA-36 manufactured by ADEKA Corporation, and the like.

Furthermore, only one kind or a mixture of two or more kinds of the component (D) may be used.

By properly selecting the type and the addition amount of the component (D), when a cured material of the sheet-shaped photocurable composition has a thickness of 150 μm or less, the yellow index of the cured material and the light transmittance of the cured material at a wavelength of 385 nm can be improved as described above. Further, by further improving these selections, even when a cured material of the photocurable composition has a thickness of 200 μm or less, in the state of being sandwiched between 0.7 mm-thick alkali-free glass plates, the light transmittance of the cured material at a wavelength of 385 nm can be maintained at 5.0% or less, and the yellow index (yellowness) of the cured material can also be to 4.0 or less. The ranges of the yellow index and the light transmittance at a wavelength of 385 nm in the cured material with a thickness of 200 μm or less are the same as those of the cured material with a thickness of 150 μm or less.

Furthermore, the lower limit value of the yellow index is 0, and the lower limit value of the light transmittance at a wavelength of 385 nm is 0%.

The light transmittance at a wavelength of 385 nm and the yellow index (yellowness) can be measured by a visible/ultraviolet spectroscopy method and calculated.

The light transmittance at a wavelength of 385 nm can be measured by the following method. First, a sheet-shaped photocurable composition sandwiched between alkali-free glass plates with a thickness of 0.7 mm×a width of 100 mm×a length of 100 mm is prepared, and irradiated with ultraviolet rays having an integrated light amount of 30 kJ/m² to manufacture a test piece in which two sheets of alkali-free glass are stuck with a cured material of the sheet-shaped photocurable composition. Then, a light transmittance can be determined by performing a light transmittance measurement according to a visible/ultraviolet spectroscopy method using the test piece, and reading the light transmittance (%) at a wavelength of 385 nm. Here, UV-2450 manufactured by Shimadzu Corporation can be used as a visible/ultraviolet spectrophotometer. Further, the details of the measuring method will be described in Examples.

The yellow index can be measured by the following method. First, a sheet-shaped photocurable composition sandwiched between alkali-free glass plates with a thickness of 0.7 mm×a width of 100 mm x a length of 100 mm is prepared, and irradiated with ultraviolet rays having an integrated light amount of 30 kJ/m² to manufacture a test piece in which two sheets of alkali-free glass are stuck with a cured material of the sheet-shaped photocurable composition. Then, a light transmittance can be calculated in accordance with JIS K7373-2006 by performing a light transmittance measurement at a wavelength of the range of 800 nm to 300 nm by the light transmittance measurement according to a visible/ultraviolet spectroscopy method using the test piece. Here, UV-2450 manufactured by Shimadzu Corporation can be used as a visible/ultraviolet spectrophotometer. Further, the details of the measuring method will be described in Examples.

The addition amount (content) of the component (D) in the photocurable composition is not particularly limited, but is preferably 0.1 to 5.0 parts by mass, more preferably 0.5 to 4.5 parts by mass, and still more preferably 1.0 to 4.0 parts by mass with respect to 100 parts by mass of the total mass of the components (A) to (C). When the addition amount is 0.1 parts by mass or more, ultraviolet rays that enter the cured material can be further cut. Further, when the addition amount is 5.0 parts by mass or less, the yellow index (yellowness) of the cured material can be further lowered.

[Component (E)]

The sheet-shaped photocurable composition according to one aspect of the present invention may further include a component (E): an auxiliary ultraviolet absorber which is an ultraviolet absorber not corresponding to the component (D) (that is, the component (D) is excluded).

In a case where the auxiliary ultraviolet absorber which is the component (E) is added to a sheet-shaped photocurable composition including the components (A) to (C), including no component (D), it is an ultraviolet absorber which cannot allow a yellow index of a cured material of the composition to be 4.0 or less, and a light transmittance of the cured material at a wavelength of 385 nm to be 5.0% or less when the cured material is obtained after photocuring the composition and has a thickness of 150 μm. Here, the component (E) is not particularly limited, but is preferably an ultraviolet absorber which can allow a yellow index of a cured material of a sheet-shaped photocurable composition including the components (A) to (E) to be 3.0 or less and a light transmittance of the cured material at a wavelength of 385 nm to be 5.0% or less when the cured material is obtained after photocuring the composition and has a thickness of 150 μm. In other words, in a case where the component (E) is added to a sheet-shaped photocurable composition including the components (A) to (D), it is preferably an ultraviolet absorber which can allow a yellow index of a cured material of the composition and a light transmittance of the cured material at a wavelength of 385 nm to be in the ranges, respectively when the cured material is obtained after photocuring the composition and has a thickness of 150 μm.

It is preferable to use the component (E) together with the component (D) from the viewpoint that the yellow index (yellowness) of the photocurable composition can be further lowered. From this, as a preferred aspect of the present invention, a sheet-shaped photocurable composition which further includes the component (E) in addition to the components (A) to (D), wherein, when a cured material obtained after photocuring the photocurable composition has a thickness of 150 μm, a yellow index of the cured material is 3.0 or less, and a light transmittance of the cured material at a wavelength of 385 nm is 5.0% or less may be mentioned.

Furthermore, the lower limit values of the yellow index and the transmittance are 0.

In addition, the auxiliary ultraviolet absorber relating to the component (E) is not particularly limited, but is preferably a compound represented by the following general formula 2.

Here, R² _(n) represents the presence of n R² groups, R²'s each independently represent a hydrocarbon group, and n represents an integer of 0 to 4.

Here, the hydrocarbon group is not particularly limited, but is preferably a hydrocarbon group having 1 to 8 carbon atoms, more preferably a hydrocarbon group having 5 to 8 carbon atoms, still more preferably a hydrocarbon group having 8 carbon atoms, and particularly preferably a tert-octyl group. In addition, n is preferably 1, 2 or 3, more preferably 1 or 2, and still more preferably 1.

Moreover, the compound represented by the general formula 2 may include a derivative thereof, in which hydrogen in the main skeleton represented by the general formula 2 is substituted with another organic group. However, it is not construed to include a multimer in which a plurality of the structures represented by the general formula 2 are bonded to each other.

Specific examples of the component (E) are not particularly limited, but include, are not limited to, for example, 2-(2′-hydroxy-5′-tert-octylphenyl)benzotriazole, 2-(3,5-di-tert-amyl-2-hydroxyphenyl)benzotriazole, and the like.

As the component (E), either a commercially available product or a synthetic product may be used. Specific examples of the commercially available product include, but are not limited to, JF-83 manufactured by Johoku Chemical Co., Ltd., SEESORB (registered trademark) 704 manufactured by Cypro Chemical Co., Ltd., and the like.

Furthermore, only one kind or a mixture of two or more kinds of the component (E) may be used.

The addition amount (content) of the component (E) in the photocurable composition is not particularly limited, but is preferably 0.1 to 3.0 parts by mass, more preferably 0.5 to 3.0 parts by mass, and still more preferably 1.0 to 2.5 parts by mass with respect to 100 parts by mass of the total mass of the components (A) to (C). When the addition amount is 0.1 parts by mass or more, ultraviolet rays that enter the cured material can be further cut. Further, when the addition amount is 3.0 parts by mass or less, the yellow index (yellowness) can be further lowered.

In addition, the total addition amount (total content) of the component (D) and the component (E) is not particularly limited, but is preferably 0.1 to 5.0 parts by mass, more preferably 0.5 to 5.0 parts by mass, and still more preferably 1.0 to 4.0 parts by mass with respect to 100 parts by mass of the total mass of the components (A) to (C). When the total addition amount is 0.1 parts by mass or more, it becomes more difficult for the cured material to transmit ultraviolet rays from the outside. Further, when the total addition amount is 5.0 parts by mass or less, it becomes easy to make a cured material more colorless, and simultaneously, a decrease in the photocurability is further inhibited.

[Other Components]

As other components, additives other than the components (A) to (E), such as a silane coupling agent, a filler such as an inorganic filler, an organic filler, and the like, a storage stabilizer, an antioxidant, a light stabilizer, an adhesion aid, a plasticizer, a dye, a pigment, a flame retardant, a sensitizer, a thermal initiator, a heavy metal deactivator, an ion trapping agent, an emulsifier, a water dispersion stabilizer, an antifoamer, a mold release agent, a leveling agent, a wax, a rheology control agent, a surfactant, and the like may be blended into the sheet-shaped photocurable composition according to one aspect of the present invention within a range that does not impair the purpose of the present invention.

(Silane Coupling Agent)

Specific examples of the silane coupling agent are not particularly limited, but include glycidyl group-containing silane coupling agents such as 2-(3,4-epoxycyclohexyl)ethyltrimethoxysilane, 3-glycidoxypropyltriethoxysilane, 3-glycidoxypropylmethyldimethoxysilane, 3-glycidoxypropyltrimethoxysilane, 3-glycidoxypropylmethyldiethoxysilane, and the like; vinyl group-containing silane coupling agents such as vinyltris(β-methoxyethoxy)silane, vinyltriethoxysilane, vinyltrimethoxysilane, and the like; (meth)acrylic group-containing silane coupling agents such as γ-(meth)acryloxypropyltrimethoxysilane (also known as 3-(meth)acryloxypropyltrimethoxysilane) and the like; amino group-containing silane coupling agents such as N-β-(aminoethyl)-γ-aminopropyltrimethoxysilane, γ-aminopropyltriethoxysilane, N-phenyl-γ-aminopropyltrimethoxysilane, and the like; others such as γ-mercaptopropyltrimethoxysilane, γ-chloropropyltrimethoxysilane, and the like. Among these, the epoxy group- or (meth)acryloyl group-containing silane coupling agents (the glycidyl group-containing silane coupling agent or the (meth)acryloyl group-containing silane coupling agent) are preferably used from the viewpoint that further improved adhesion can be expected. Among these, the (meth)acryloyl group-containing silane coupling agent is more preferable, 3-(meth)acryloxypropyltrimethoxysilane is still more preferable, and 3-methacryloxypropyltrimethoxysilane is particularly preferable. These may be used singly or in combination of two or more kinds thereof. The blending amount (addition amount, content) of the silane coupling agent is not particularly limited, but is preferably 0.01 to 10 parts by mass with respect to 100 parts by mass of the total of the components (A) to (D) (or (E)).

(Inorganic Filler)

Specific examples of the inorganic filler are not particularly limited, but include glass powder, fumed silica powder, silica powder, alumina powder, mica powder, silicone rubber powder, calcium carbonate powder, aluminum nitride powder, carbon powder, kaolin clay powder, dry clay mineral powder, dry diatomaceous earth powder, metal powder, and the like. Further, examples of the fumed silica powder among those include those whose surface is chemically modified (hydrophobicized) with, for example, organochlorosilanes, polyorganosiloxane, hexamethyldisilazane, and the like. Specific examples of a commercially available product of the fumed silica powder include, but are not limited to, Aerosil (registered trademark) series R974, R972, R972V, R972CF, R805, R812, R812S, R816, R8200, RY200, RX200, RY200S, R202, and the like, manufactured by Nippon Aerosil Co., Ltd. These may be used singly or in combination of two or more kinds thereof. The blending amount (addition amount, content) of the inorganic filler is not particularly limited, but from the viewpoint of improving the fluidity and the like and further improving the mechanical strength of a cured material, it is preferably 0.1 to 100 parts by mass with respect to 100 parts by mass of the total of the components (A) to (D) (or (E)).

[Solvent]

In one aspect of the present invention, a solvent can be used as necessary to mix the respective components of the photocurable composition and to process the photocurable composition into a sheet shape.

Examples of the solvent include alcohols such as methanol, ethanol, and the like; chlorine-based solvents such as dichloroethane, trichloroethane, and the like; fluorine-based solvents such as trichlorofluoroethane and the like; ketone-based solvents such as acetone, methyl ethyl ketone, methyl isobutyl ketone, and the like; ester-based solvents such as methyl acetate, ethyl acetate, propyl acetate, butyl acetate, and the like; ethers such as dimethyl ether, methyl ethyl ether, and the like; hydrocarbon-based solvents such as pentane, hexane, heptane, cyclohexane, and the like; aromatic solvents such as benzene, toluene, xylene, and the like; and so on. Among these, the ketone-based solvent is preferable, and methyl ethyl ketone is more preferable, in consideration of the compatibility with the component (B) and the component (C).

The addition amount of the solvent is not particularly limited, but is preferably 50 to 200 parts by mass with respect to 100 parts by mass of the total mass of the components (A) to (E). Within this range, it becomes easier to obtain a film thickness of 200 μm or less upon molding into a sheet shape.

[Method for Preparing Photocurable Composition]

The method for preparing a photocurable composition is not particularly limited, and the photocurable composition can be obtained by mixing the respective components by a known mixing method. When mixing, a solvent may be used as described above. In a case where the solvent is used, when the solvent is volatilized during mixing, it is preferable to supplement the volatilized solvent.

As a preferred aspect of the present invention, a method for preparing a sheet-shaped photocurable composition, including mixing the components (A) to (D), in which the type and the addition amount of the component (D) used in the mixing are selected such that when a cured material obtained after curing the photocurable composition has a thickness of 150 μm, a yellow index of the cured material is 4.0 or less and a light transmittance of the cured material at a wavelength of 385 nm is 5.0% or less, may be mentioned.

Furthermore, as a more preferred aspect of the present invention, a method for preparing a sheet-shaped photocurable composition, including mixing the components (A) to (E), in which the types and the addition amounts of the component (D) and the component (E) used in the mixing are selected such that when a cured material obtained after curing the photocurable composition has a thickness of 150 μm, a yellow index of the cured material is 3.0 or less and a light transmittance of the cured material at a wavelength of 385 nm is 5.0% or less, may be mentioned.

In addition, in the selection of the types and the addition amounts of the component (D) and the component (E) in the preparation of the photocurable composition according to these preparation methods, preferred ranges of desired yellow indices and light transmittances at a wavelength of 385 nm are the same as those described in the description of the photocurable composition above.

As a method for processing the photocurable composition into a sheet shape (a method for preparing a sheet-shaped photocurable composition), a known technique can be used. For example, a method in which a solvent is added to the photocurable composition to prepare a stock solution whose viscosity is intentionally reduced, the stock solution is coated onto a mold-released film whose surface has been release-treated in advance, and then the solvent is dried to perform a processing into a sheet shape may be mentioned.

As the coating step, a known coating method can be used, and specific examples thereof include, but are not limited to, a flow coating method, a roll coating method, a gravure roll method, a wire bar method, a lip die coating method, and the like. Further, as the drying step, a known drying method can be used. A drying device in this step is not particularly limited, a known device can be used, and examples thereof include a hot air drying furnace, an IR furnace, and the like.

The sheet-shaped photocurable composition thus formed as above may be formed on the mold-released film as described above, or the mold-released film may be stuck to the other surface. Further, in a case where the mold-released film is not used at the time of application, or in a case where a mold-released film other than the mold-released film used at the time of application is used, the mold-released film may be stuck to one surface or both surfaces of the sheet-shaped photocurable composition.

A material of the mold-released film is not particularly limited, and examples thereof include plastic films such as polyethylene, polypropylene, polyethylene terephthalate, and polyester films, and the like, paper, cloth, non-woven fabric, and the like. Among these, the plastic films are preferable from the viewpoint of mold releasability. The thickness of the mold-released film is preferably 5 to 300 μm, and more preferably 25 to 200 μm. The mold-released film is preferably one which has been subjected to a mold release treatment with a fluorine-based compound, a silicone-based compound, a long-chain alkyl-based compound, or the like.

Depending on the thickness of the sheet-shaped photocurable composition, the thickness and the colored state of a cured material of the sheet-shaped photocurable composition varies, and the thinner the cured material, the more difficult it is to color. Therefore, the upper limit of the film thickness of the sheet-shaped photocurable composition is not particularly limited, but is preferably 200 μm or less, and more preferably 150 μm or less. In addition, as the sheet-shaped photocurable composition has a higher thickness, the cutting capability of the cured material against ultraviolet rays is proportionally improved. Thus, the lower limit of the film thickness of the sheet-shaped photocurable composition is not particularly limited, but is preferably 10 μm or more. Here, as described above, as a characteristic of the cured material, it is particularly preferable that when a cured material has a thickness of 200 μm or less, in the state of being sandwiched between alkali-free glass plates with a thickness of 0.7 mm, a light transmittance is 5.0% or less at a wavelength of 385 nm, and a yellow index (yellowness) is 3.0 or less. In addition, the alkali-free glass plate is not particularly limited, but for example, 1737, Eagle 2000, Eagle XG, and the like, manufactured by Corning Incorporated, can be used.

<Cured Material and Method for Preparing the Same>

The sheet-shaped photocurable composition according to one aspect of the present invention can be cured by irradiation with energy rays such as ultraviolet rays, visible light, and the like. That is, the cured material according to one aspect of the present invention can be prepared by irradiating the sheet-shaped photocurable composition with energy rays such as ultraviolet rays, visible light, and the like.

The contents of the respective constituents derived from the components (A) to (E) and the other components in the cured material will be substantially the same as the contents of the components (A) to (E) and the other components.

The irradiated light used for the irradiation of energy rays is not particularly limited and varies depending on the formulation of the photocurable composition, but irradiated light in the wavelength range of 150 to 750 nm is usually preferable. Further, an irradiation device is not particularly limited and known devices can be used, depending on a desired wavelength, but examples thereof include a low-pressure mercury lamp, a medium-pressure mercury lamp, a high-pressure mercury lamp, an ultrahigh-pressure mercury lamp, a xenon lamp, a metal halide lamp, an LED lamp, and the like. Among these, the high-pressure mercury lamp is preferable from the viewpoint of the characteristics of a light used, for example, viewpoints of curability, curing efficiency, and the like. Irradiation conditions are not particularly limited and vary depending on the formulation of the photocurable composition, but the integrated light amount is usually preferably 1 to 100 kJ/m², more preferably 5 to 70 kJ/m², and still more preferably 10 to 50 kJ/m².

A use of the sheet-shaped photocurable composition according to one aspect of the present invention is not particularly limited, but the sheet-shaped photocurable composition is preferably used for assembling a display device such as a liquid crystal display, an organic EL display, and the like. Specifically, the sheet-shaped photocurable composition according to one aspect of the present invention is suitable for assembling a display element, a cover panel, a touch panel, or the like into a display device, or for assembling an organic EL element itself.

As described above, a mold-released film may be stuck to one surface or both surfaces of the sheet-shaped photocurable composition according to one aspect of the present invention. Here, a step of adhering two transparent adherends using a sheet-shaped photocurable composition having a mold-released film stuck to one surface thereof (adhering step) such as a case where a mold-released film on one surface of a sheet-shaped photocurable composition having mold-released films stuck to both surfaces thereof is peeled, and other cases will be described below.

The adhering step preferably includes a laminating step and a curing step.

In the laminating step, it is preferable that sticking (transferring) is performed while thereof applying pressure and heat with a laminator in the state where one side of the sheet-shaped photocurable composition, not covered by a mold-released film, is attached to one adherend. Further, next, it is preferable that the mold-released film is peeled and the other adherend is stuck with a laminator in the same manner. Here, the laminating pressure is not particularly limited and can be appropriately adjusted. Further, the laminating temperature is not particularly limited, but is preferably 50 to 100° C. As a device used for performing the sticking, a vacuum press machine, a vacuum laminator, an autoclave, or the like which can performing the sticking in vacuum or a reduced pressure atmosphere may be used instead of the laminator.

In the curing step, a laminate (laminate constituted with the adherend/the sheet-shaped photocurable composition/the adherend) after lamination can be irradiated with energy rays to cure the sheet-shaped photocurable composition, thereby sticking the two adherends. The details of irradiation with energy rays are the same as those described above.

However, the adhering step is not limited to this.

EXAMPLES

Hereinafter, the present invention will be described in more detail with reference to Examples, but the present invention is not limited to these Examples.

Hereinafter, the “photocurable composition” is also simply referred to as a “composition”, and the “sheet-shaped photocurable composition” is also simply referred to as a “sheet”.

Examples 1 to 3 and Comparative Examples 1 to 8

The following respective components were prepared in order to prepare a photocurable composition.

<<Component (A): (Meth)Acrylate Compound>>

A urethane-modified acrylate oligomer (50%-by-mass diluted product of isobornyl methacrylate, weight-average molecular weight of 65,000) (UN-004RU, manufactured by Negami Chemical Industrial Co., Ltd.) having polycarbonate in the main skeleton;

-   -   Polyethylene glycol #1000 dimethacrylate (molecular weight of         1, 136) (NK ESTER 23G, manufactured by Shin-Nakamura Chemical         Co., Ltd.);     -   Polyethylene glycol #600 dimethacrylate (molecular weight         of 736) (NK ESTER 14G, manufactured by Shin-Nakamura Chemical         Co., Ltd.).

<<Component (B): Film Forming Resin>>

-   -   Mixed type (solid content of 100%) of bisphenol A type phenoxy         resin/bisphenol F type phenoxy resin with a weight-average         molecular weight of 60,000 (jER (registered trademark) 4250,         manufactured by Mitsubishi Chemical Corporation).

<<Component (C): Photoinitiator>>

-   -   2,4,6-Trimethylbenzoyl-diphenyl-phosphine oxide (IRGACURE         (registered trademark) TPO, manufactured by BASF).

<<Component (D): Compound Represented by the General Formula 1 (Ultraviolet Absorber)>>

2-(5-Chloro-2-benzotriazolyl)-6-tert-butyl-p-cresol (ADEKA STAB (registered trademark) LA-36, manufactured by ADEKA Corporation).

<<Component (E): Ultraviolet Absorber Other than the Component (D) (Including the Compound Represented by the General Formula 2)>>

-   -   2,2′,4,4′-Tetrahydrobenzophenone (Uvinul (registered trademark)         3050 manufactured by BASF);     -   2-(2′-Hydroxy-5′-tert-octylphenyl)benzotriazole (JF-83,         manufactured by Johoku Chemical Co., Ltd.);     -   2-(3,5-di-tert-Amyl-2-hydroxyphenyl)benzotriazole (SEESORB         (registered trademark) 704, manufactured by Cipro Chemical Co.,         Ltd.);         2-(2′-Hydroxy-5′-methacryloxyethylphenyl)-2H-benzotriazo le         (RUVA-93, manufactured by Otsuka Chemical Co., Ltd.);         6-(2-Benzotriazolyl)-4-tert-octyl-6′-tert-butyl-4′-methy         1-2,2′-methylenebisphenol (JAST-500, manufacturedbyJohoku         Chemical Co., Ltd.).

<<Other Components: Compounds Other than the Components (A) to (E)>>

-   -   Ethyl 2-cyano-3,3-diphenylacrylate (SEESORB (registered         trademark) 501 manufactured by Cipro Chemical Co., Ltd.);     -   2-Ethylhexyl 2-cyano-3,3-diphenylacrylate (SEESORB (registered         trademark) 502 manufactured by Cypro Kasei Co., Ltd.).

<<Coupling Agent>>

-   -   3-Methacryloxypropyltrimethoxysilane (KBM-503, manufactured by         Shin-Etsu Chemical Co., Ltd.)

<<Solvent>>

-   -   Methyl ethyl ketone (reagent).

The components (A) to (E), the other components, and the solvent were weighed and added to a stirring vessel, and stirred in an atmosphere at 25° C. for 1 hour. At this time, if methyl ethyl ketone (solvent) was volatilized from the total weight before stirring, a volatilized amount of methyl ethyl ketone was supplemented. The detailed preparation amount was in accordance with Table 1 below. All the numerical values for the addition amount in Table 1 below are expressed in parts by mass. Further, the addition amount (parts by mass) of the component (D) with respect to 100 parts by mass of the total of the components (A) to (C), and the addition amount (parts by mass) of the component (E) with respect to 100 parts by mass of the total of the components (A) to (C) are also shown in Table 1 below. The blank columns in Table 1 indicate that the components were not added.

Using a coating machine, the composition solutions according to Examples 1 to 3 and Comparative Examples 1 to 8 in Table 1 below were each coated onto a mold-released film with a clearance of 200 μm. Subsequently, the composition was dried at a speed of 500 mm/min through a drying line of 1.5 m in length in an atmosphere at 80° C. and two drying lines of 1.5 m in length in an atmosphere at 110° C. to form the composition into a sheet shape.

Thereafter, another mold-released film was stuck to the surface of the sheet (composition) to manufacture a laminated sheet having two types of mold-released films provided on both surfaces of the composition.

With regard to the obtained laminated sheet, the film thickness inclusive of the mold-released film was measured having a thickness gauge, and the thicknesses of the two types of the mold-released films known in advance were subtracted therefrom to calculate the thickness of the sheet (composition). This value is shown in Table 1 below as “Film thickness (after drying)”. The unit of the film thickness in Table 1 below is (μm).

In addition, in drying for volatilizing the solvent, the solvent is dried from the surface, and thus, it becomes difficult for the internal solvent to volatilize. Therefore, from the viewpoint that when the film thickness is increased, bubbles remain inside the coating film, it is preferable that the clearance is 300 μm or less (lower limit: more than 0 μm).

TABLE 1 Example Example Example Comparative Comparative Comparative Component Raw material 1 2 3 Example 1 Example 2 Example 3 Component (A) UN-004RU 96 96 96 96 96 96 NK ESTER 23G 1.3 1.3 1.3 1.3 1.3 1.3 NK ESTER 14G 2.7 2.7 2.7 2.7 2.7 2.7 Component (B) jER4250 34.0 34.0 34.0 34.0 34.0 34.0 Component (C) TPO 1.0 1.0 1.0 1.0 1.0 1.0 Component (D) LA-36 1.3 2.7 0.8 Component (E) Uvinul3050 2.7 JF-83 1.3 1.3 SEESORB704 RUVA-93 JAST-500 Other SEESORB501 components SEESORB502 Coupling agent KBM-503 1.3 1.3 1.3 1.3 1.3 1.3 Solvent Methyl ethyl ketone 140.0 140.0 140.0 140.0 140.0 140.0 Total 277.6 279.0 278.4 276.3 279.0 277.6 Addition amount of component (D) 1.0 2.0 0.6 0.0 0.0 0.0 with respect to 100 parts by mass of total of components (A) to (C) Addition amount of component (E) 0.0 0.0 1.0 0.0 2.0 1.0 with respect to 100 parts by mass of total of components (A) to (C) Film thickness (after drying) 150 150 150 150 150 150 Comparative Comparative Comparative Comparative Comparative Component Raw material Example 4 Example 5 Example 6 Example 7 Example 8 Component (A) UN-004RU 96 96 96 96 96 NK ESTER 23G 1.3 1.3 1.3 1.3 1.3 NK ESTER 14G 2.7 2.7 2.7 2.7 2.7 Component (B) jER4250 34.0 34.0 34.0 34.0 34.0 Component (C) TPO 1.0 1.0 1.0 1.0 1.0 Component (D) LA-36 Component (E) Uvinul3050 JF-83 SEESORB704 2.7 RUVA-93 2.7 JAST-500 1.3 Other SEESORB501 1.3 components SEESORB502 1.3 Coupling agent KBM-503 1.3 1.3 1.3 1.3 1.3 Solvent Methyl ethyl ketone 140.0 140.0 140.0 140.0 140.0 Total 279.0 279.0 277.6 277.6 277.6 Addition amount of component (D) 0.0 0.0 0.0 0.0 0.0 with respect to 100 parts by mass of total of components (A) to (C) Addition amount of component (E) 2.0 2.0 1.0 0.0 0.0 with respect to 100 parts by mass of total of components (A) to (C) Film thickness (after drying) 150 150 150 150 150

Using the laminated sheets formed from the compositions according to Examples 1 to 3 and Comparative Examples 1 to 8, confirmation of the photocurability, confirmation of the appearance (after curing), measurement of a light transmittance (after curing), and measurement of a yellowness (after curing) as shown below were performed. The Nos. of the compositions in Table 1 above are also reflected as they on the sheets, and using the Nos. as the sheet Nos., the evaluation results are shown in Table 2 below.

[Confirmation of Photocurability]

Using a belt conveyor type ultraviolet irradiator, a laminated sheet with a length of 30 mm x a width of 30 mm was subjected to light irradiation (ultraviolet irradiation) with a high-pressure mercury lamp under the condition of an integrated light amount of 30 kJ/m² to cure the composition portion. Next, the obtained cured material was rounded into a cylindrical shape having a diameter of 3 mm and placed in a hot air drying furnace in an atmosphere of 80° C. for 5 minutes. Then, the temperature was dropped to room temperature, then the cured material was visually confirmed, and the “photocurability” was evaluated according to the following evaluation criteria. Here, a case where the heating causes softening or melting such that the cylindrical shape cannot be maintained is evaluated as “X”, and it can thus be said that the photocuring is not sufficient:

<<Evaluation Criteria>>

◯: The cylindrical shape is maintained.

X: The cylindrical shape is not maintained.

[Confirmation of Appearance (after Curing)]

With regard to a laminated sheet from which one mold-released film was peeled, an alkali-free glass plate with a thickness of 0.7 mm×a width of 100 mm×a length of 100 mm was attached to the peeled surface of the composition, and subjected to transferring using a heat roll laminator with a roll temperature set to 80° C. Subsequently, the other mold-released film was peeled from the laminated sheet on the alkali-free glass plate, and the same alkali-free glass plate as described above was stuck to the peeled surface of the composition, and subjected to sticking in an atmosphere of 80° C., using a vacuum laminator. Then, using a belt conveyor type ultraviolet irradiator, the laminated sheet was irradiated with ultraviolet rays in an integrated light amount of 30 kJ/m² by a high-pressure mercury lamp to manufacture a test piece in which two sheets of alkali-free glass were stuck with a sheet (that is, two sheets of alkali-free glass were adhered via a cured material of the sheet (composition)). Thereafter, the appearance of the test piece was visually confirmed and the “Appearance (after curing)” was evaluated according to the following evaluation criteria. Here, “◯” corresponding to an evaluation showing a state in which the component (D) and the component (E) are dissolved to ensure transparency is preferable:

<<Evaluation Criteria>>

◯: The components are dissolved and nothing remains.

X: The components are dissolved and some remain.

[Measurement of Light Transmittance (after Curing)]

Using the same test piece as the test piece manufactured in the evaluation of “Confirmation of Appearance (after Curing)” above, measurement of a light transmittance according to visible/ultraviolet spectroscopy was performed using a visible/ultraviolet spectrophotometer UV-2450 manufactured by Shimadzu Corporation. Specifically, measurement of a light transmittance at a wavelength of the range of 800 nm to 300 nm was performed, and the light transmittance (%) at a wavelength of 385 nm was read. Then, with a number of tests set to n=3, an average value was calculated, and evaluation of the results was performed in terms of “Light transmittance (after curing) (unit: %)” according to the following evaluation criteria. In a case where the evaluation result in the evaluation of “Confirmation of Appearance (after Curing)” is “X”, the present measurement was not performed and the result was expressed as “-”. The evaluation result of the light transmittance at a wavelength of 385 nm for sufficiently cutting the ultraviolet rays that damage the adherend is “◯”, and the numerical value is 5.0% or less, preferably 3.0% or less, and most preferably 1.0% or less. In addition, the present measurement is in accordance with JIS K 7373-2006:

<<Evaluation Criteria>>

◯: The light transmittance at a wavelength of 385 nm is 5% or less.

X: The light transmittance at a wavelength of 385 nm is more than 5%.

[Measurement of Yellowness (Yellow Index) (after Curing)]

Using the same test piece as the test piece manufactured in the evaluation of “Confirmation of Appearance (after Curing)” above, measurement of a yellowness according to a visible/ultraviolet spectroscopy method was performed using a visible/ultraviolet spectrophotometer UV-2450 manufactured by Shimadzu Corporation. Specifically, measurement of a light transmittance at a wavelength of the range of 800 nm to 300 nm was performed, and the yellowness was calculated in accordance with JIS K 7373-2006. With a number of tests set to n=3, an average value was calculated, and evaluation of the results was performed in terms of “Yellowness (after curing)” according to the following evaluation criteria. The evaluation result of the yellowness for realizing colorlessness and transparency is “◯”, and the numerical value is 4.0 or less.

<<Evaluation Criteria>>

◯: The yellowness is 4.0 or less.

X: The yellowness is more than 4.0.

TABLE 2 Example Example Example Comparative Comparative Comparative Test items 1 2 3 Example 1 Example 2 Example 3 Photocurability ◯ ◯ ◯ ◯ ◯ ◯ Appearance ◯ ◯ ◯ ◯ ◯ ◯ (after curing) Light 0.0 0.1 0.4 86.5 0.3 24.8 transmittance ◯ ◯ ◯ X ◯ X (after curing) Test items 3.7 3.6 2.5  0.8 4.8  2.0 ◯ ◯ ◯ ◯ X ◯ Comparative Comparative Comparative Comparative Comparative Test items Example 4 Example 5 Example 6 Example 7 Example 8 Photocurability ◯ ◯ ◯ ◯ ◯ Appearance ◯ ◯ ◯ ◯ ◯ (after curing) Light 7.8 35.5 37.5 50.2 48.4 transmittance X X X X X (after curing) Test items 3.3  3.3  2.0  1.4  1.3 ◯ ◯ ◯ ◯ ◯

Since Comparative Example 1 is a cured material which does not include the component (D) and the component (E) at all, the yellowness is very low, but on the other hand, the light transmittance is very high and ultraviolet rays cannot be sufficiently cut from the outside.

From the viewpoint of the light transmittance, the cured materials of Examples 1 to 3 and Comparative Example 2 have a light transmittance of 5.0% or less and a sufficient ultraviolet ray cutting capability, whereas the other cured materials have a high light transmittance and cannot cut ultraviolet rays sufficiently from the outside. Here, it is determined that when the light transmittance is 5.0% or less, ultraviolet rays from the outside can be sufficiently cut in practical use.

According to the comparison of the yellownesses of the cured materials of Examples 1 to 3, and Comparative Example 2, in Comparative Example 2, the yellowness exceeds 4.0, which is different from those in Examples 1 to 3. When the yellowness exceeds 4.0, the cured material will have a strong yellowish tint even upon visual recognition. Further, in Examples 1 to 3, it is found that the yellowness in Example 3 including both the component (D) and the component (E) is even lower than those in Examples 1 and 2.

INDUSTRIAL APPLICABILITY

The present invention can be suitably used for assembling a display device such as a liquid crystal display, an organic EL display, and the like. Specifically, the present invention is suitable for assembling a display element, a cover panel, a touch panel, or the like into a display device, or for assembling an organic EL element itself, and thus, it can inhibit the deterioration of the organic EL element due to ultraviolet rays from the outside.

This application is based on Japanese Patent Application No. 2018-103002, filed on May 30, 2018, the disclosure content of which is hereby incorporated as its entirety by reference. 

1. A sheet-shaped photocurable composition comprising the following components (A) to (D), and when a cured material obtained after photocuring the photocurable composition has a thickness of 150 μm, a yellow index of the cured material is 4.0 or less and a light transmittance of the cured material at a wavelength of 385 nm is 5.0% or less: a component (A): a (meth)acrylate compound, a component (B): a film forming resin, a component (C): a photoinitiator, and a component (D): an ultraviolet absorber.
 2. The sheet-shaped photocurable composition according to claim 1, wherein the component (D) is a compound represented by the following general formula 1:

wherein R¹ _(n) represents the presence of n R¹ groups, R¹'s each independently represent a hydrocarbon group, and n represents an integer of 0 to
 4. 3. The sheet-shaped photocurable composition according to claim 1, wherein the amount of the component (D) is 0.1 to 3.0 parts by mass with respect to 100 parts by mass of the total mass of the components (A) to (C).
 4. The sheet-shaped photocurable composition according to claim 1, further comprising the following component (E), and when a cured material obtained after photocuring the photocurable composition has a thickness of 150 μm, a yellow index of the cured material is 3.0 or less and a light transmittance of the cured material at a wavelength of 385 nm is 5.0% or less: a component (E): an auxiliary ultraviolet absorber that is an ultraviolet absorber not corresponding to the component (D) (that is, excluding the component (D)).
 5. The sheet-shaped photocurable composition according to claim 4, wherein the component (E) is a compound represented by the following general formula 2:

wherein R² _(n) represents the presence of n R² groups, R²'s each independently represent a hydrocarbon group, and n represents an integer of 0 to
 4. 6. The sheet-shaped photocurable composition according to claim 4, wherein the total mass of the component (D) and the component (E) is 0.1 to 3.0 parts by mass with respect to 100 parts by mass of the total mass of the components (A) to (C).
 7. The sheet-shaped photocurable composition according to claim 1, wherein the component (A) includes a (meth)acrylate oligomer and a (meth)acrylate monomer.
 8. The sheet-shaped photocurable composition according to claim 1, wherein the component (B) is a phenoxy resin.
 9. A cured material of the sheet-shaped photocurable composition according to claim
 1. 